Ion implantation is a process of depositing chemical species into a substrate by direct bombardment of the substrate with energized ions. In semiconductor manufacturing, ion implanters are used primarily for doping processes that alter the type and level of conductivity of target materials. A precise doping profile in an integrated circuit (IC) substrate and its thin-film structure is often crucial for proper IC performance. To achieve a desired doping profile, one or more ion species may be implanted in different doses and at different energy levels.
To form devices on a semiconductor wafer, it is usually necessary to implant impurities at different depths of the semiconductor wafer. The energy of impurities in an ion beam directed toward the semiconductor wafer is determinative of the depth to which the impurities penetrate into the semiconductor wafer. As devices are reduced in size and their operating speeds are increased, it has become desirable to use very low energy ion beams to form, for example, shallow transistor junctions in the semiconductor wafer.
At the same time, high energy ion implantation may help minimize production costs because high energy ion implantation does not require some conventional processes, such as, but not limited to, the masking of a semiconductor wafer, to be performed. Also, semiconductor devices manufactured through the use of high energy ion implantation may exhibit relatively low levels of junction leakage and improved latch-up characteristics. Thus, the production yield may be high with respect to an ion implantation process carried out by high energy ion implantation. Therefore, high energy ion implantation may be beneficial for implanting ions in at least one or more semiconductor device manufacturing processes.
FIG. 1 depicts a prior art ion implanter system 100. The ion implanter system 100 may comprise an ion source 102 and a complex series of components through which an ion beam 10 passes. The series of components may include, for example, an extraction manipulator 104, a filter magnet 106, an acceleration or deceleration column 108, an analyzer magnet 110, a rotating mass slit 112, a scanner 114, and a corrector magnet 116. The ion source 102, the extraction manipulator 104, and the filter magnet 106 may be housed in a terminal 118. Much like a series of optical lenses that manipulate a light beam, the ion implanter components can filter and focus the ion beam 10 before steering it towards an end station 120. The ion implanter components that can filter and focus the ion beam 10 may be referred to as optical elements, or beam optics.
The acceleration or deceleration column 108 is a critical component to the ion implanter system 100. As the range of required energy levels for the ion beam 10 may be wide (e.g., from about 1 kV to above 600 kV), the acceleration or deceleration column 108 may be required to accelerate or decelerate ions using a wide voltage spectrum (e.g., from about 1 kV to above 600 kV).
Conventionally, a resistive divider may be used to gradually accelerate (divide the acceleration potential) or decelerate (divide the deceleration potential) the ion beam 10 along the column 108. That is, one or more resistors may be electrically connected between adjacent electrodes along the column 108. A plurality of resistors may thus form a chain of resistors. Each electrode of the column 108 may be electrically connected to certain electrical contacts along the resistor chain. Thus, the acceleration or deceleration voltage may be distributed by the resistors. The distribution of voltage along the column 108 may be referred to as grading. As the operational voltage spectrum gets wider and the voltage increases, there may be concerns with the conventional resistive divider.
For example, the conventional resistive divider may use switches to select a different resistor chain with lower resistance for low energy acceleration and deceleration. The switches may be activated electrically and may be referred to as electrical switches. The electrical switches may be activated by relays, for example. The switches may also be powered by pressurized fluid and may be referred to as hydraulic/pneumatic switches. The hydraulic/pneumatic switches may be activated by pressurized media in a conduit made of dielectrical material (e.g., polytetrafluoroethylene (PTFE) air lines). However, due to a difference in dielectric constant of the conduit and surrounding air, the conduit may be subjected to high electrical stress and may cause high voltage instability of the column 108. To avoid this from happening, proper shielding and insulation of the resistive divider may be needed to ensure the proper function of the column 108.
Also, each resistor component and/or switch in the conventional resistive divider may be required to be protected against high electric field stress when the conventional resistive divider is operating in a wide range of voltages for ion implantation. For example, in a high energy mode, a high acceleration voltage (e.g., above 650 kV) may be graded over the resistor chain. Conductive materials of the resistors, such as lead or ferrule connections, may need shielding due to high electric field stress. Such shielding has previously been achieved by placing the resistor chain in a pressurized vessel that may be filled with a high dielectric strength material (e.g., SF6 gas) Also, the conventional resistive divider may arc at lower than desired voltages from airline holes. Additionally, service of the resistor chain is not easy in such a configuration as the pressurized vessel needs to be drained, which may be slow and labor intensive.
In view of the foregoing, it may be understood that there are significant problems and shortcomings associated with current technologies for controlling an accelerated or decelerated charged particle beam for ion implanters.